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A Talk on the Wild Side.

New Hampshire: Shorter Winters Mean More Ticks, Pose Big Threat to Moose

A moose with a clearly visible rib cage rests in murky water

Tick infestations can drain the blood supply of moose and can lead to malnutrition and death. In a year with average weather conditions, a moose will probably carry 30,000 ticks by late fall. In years with a late first snow fall, a moose could carry 160,000 ticks. Photo: Patrick Lafreniere. Download.

The average moose in New Hampshire stands about six feet tall at the shoulder and weighs about 1,000 pounds. Yet a creature smaller than the eraser on a pencil is a big threat to these massive animals, popular with both wildlife watchers and hunters.

The creatures posing the threat are winter ticks – Dermacentor albipictus. A New Hampshire Fish and Game Department study that began in 2001 collared and tracked moose and found winter ticks accounted for 41 percent of all moose deaths in the state over a five-year period. That was nearly the same percentage of collared moose killed by hunting and moose-vehicle collisions combined. Virtually all the calf deaths during the study were due to winter ticks.

New Hampshire Fish and Game Department researchers will spend the next several years studying the best way to accurately determine the numbers of ticks on moose and how that relates to mortality rates, as well as the changing climate.

According to a report from the Union of Concerned Scientists, “rising temperatures over the past few decades have caused snow to become wetter and decreased the average number of snow-covered days across the state.” In looking toward the future, the report says climate change could see New Hampshire’s snow season shrink by almost 50 percent by mid-century.

Unfortunately, climate change is likely to intensify this threat to moose. “There’s almost no question that warming trends are going to be good for ticks, which in turn will be bad for moose,” says Kristine Rines, moose project leader for the New Hampshire Fish and Game Department.

Winter ticks aren’t like the typical ticks that people come into contact with. In autumn, larval-stage ticks climb up vegetation in large groups and “quest” – or look for a passing animal to hop on to.

A winter tick clasped between tweezers

The winter tick, a creature smaller than a pencil eraser is a big threat to moose. Photo: University of Minnesota, Natural Resources Research Institute.

The moose don’t just get a tick or two at a time, but rather a couple hundred at a time. In a year with average weather conditions, a moose will probably carry 30,000 ticks by late fall. In years with a late first snow fall, a moose could carry 160,000 ticks.

After attaching to a moose, the ticks feed and then nap until late winter or early spring when they begin to feed again.

“This is at a time when moose are at a physiological low,” says Rines. “Suddenly they have all these insects on them, biting them, making them itch, draining their blood supply and generally making them miserable.”

At a time when moose should be resting, they’re scratching so much that it removes their coat. In addition, the itching means they’re unable to lie down and rest.

According to Rines, “Not only do the ticks remove a large portion of the blood supply of the moose, but the moose’s ability to rest at this time of year and the physiological stress of reduced blood volume lead to a compromised immune system. This combination leaves the moose open to an array of other infections.”

A healthy moose looks alert in the outdoors

A healthy moose. Photo: Ryan Haggerty, USFWS. Download.

Climate change magnifies the tick problem in a couple of ways. If there’s no snow on the ground in March or April, engorged female ticks that fall off moose survive to lay their eggs in June. That produces a larger tick population in the fall when they are ready to quest again. Warmer temperatures and less snow in the fall means the ticks can continue questing for a longer period of time, infecting moose at a higher rate.

Rines says for calves, a very high number of ticks are “almost a death sentence.” A tick-infested calf can lose its entire blood supply over a matter of months.

New Hampshire isn’t the only state witnessing rising temperatures taking a toll on moose. As noted in a previous blog post, biologists at Agassiz National Wildlife Refuge and the Minnesota Department of Natural Resources say rising temperatures are at least partly to blame for a sharp drop in moose numbers in northwest Minnesota since the early 1990s. 

Warming appears to make moose more susceptible to deer-borne parasites and ticks in Minnesota as well, often leading to malnutrition and death.


Climate Change Focus: Adaptation

Author: Frank Wolff

Contacts: Kristine Rines, 603-744-5470, Kristine.rines@wildlife.nh.gov

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